19 ability to easily consider contextual circumstances in design is very useful. For
this purpose, CAD and BIM editors should be able to assimilate information resources that may exist in different coordinate systems, and to register
georeferenced architectural detail. Information should be able to be assimilated directly from Web Map Services Imagery and thematic maps, WCS terrain and
quantitative surface data, and WFS for vector features and CityGML. It will be very helpful if CADBIM editors were able to visualize and query the semantic
information in CityGML. 2. Catalog Discovery Context Capabilities: Part of the problem and advantage of
assimilating information from OGC Web Services should be the access to the search and discovery capabilities of catalog servers. This calls to mind a need for
Catalog client functions to be built into ACADBIM Authoring Clients. Further, the references to assimilated OGC layers should be able to be saved and
exchanged via OGC Context documents. 3. Able to Export well known Exchange Formats: It is increasingly common for
CADBIM editors to be able to import and export IFC as a fully capable BIM exchange format. KML is also a common export format for lightweight portrayal.
We are also seeing the utility of encapsulated 3D document formats such as 3D PDF and DWF which perform as end-product documents from the design process.
It will be useful for CADBIM editor clients to be able to exchange information as CityGML, such as might be needed to post space planning details to a WFS-T.
4. Able to distribute efficiently enormous amount of data: Buildings can potentially have numerous details, and IFC has been designed for supporting this level of
detail. Therefore, a single multi-storey building can require 10s if not 100s of megabytes. Transferring all this data on the Web will require different techniques
Compression, levels of detail, streaming, in order to provide quickly an overall view like the shell of the building and gradually providing details if required.
The structure of IFC Express is not as suitable for this kind of incremental delivery as the IFCxml. This is a topic for more investigation in OWS-5.
4.4 CityGML and BIM Analysis Client
A large part of the value of integrating AEC workflows and exchanges with the OGC web services architecture comes in the ability to integrate BIM information related to
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Copyright © 2007 Open Geospatial Consortium. All Rights Reserved
multiple sites over broad areas. This was demonstrated in OWS-4 through modifications to the LandXplorer viewer by the Hasso-Plattner Institute. A more thorough explanation
of the implementation of this viewer is provided in Annex B of this document. 1. Able to Assimilate data from OGC Services such as WFS, WMS and WCS.
2. Able to create thematic views based on the attributes of CityGML objects: In our case it was important to be able to deal with attributes that were associated to GML
objects via property sets representing the space properties used by the general services administration. To the extent that metadata explains the character of these
properties e.g. their attribute names, it is important that these be displayed in an informative way.
3. CatalogDiscoveryContext Capabilities. See notes listed above in CADBIM Editor Clients.
4. Domain-specific analytical tasks. A chief advantage of the GMLBIM analysis client, which takes its input as CityGML, as opposed to more visualization-oriented
clients that may use more streamlined exchange formats such as X3D or KML, is that the semantic and topological information capabilities of the CityGML information
model may be used with local programming logic that may be applied to study aspects the aggregation of built assets in over a broad area. Such questions may be
related to space planning, as we demonstrated in OWS-4, but might also involve such questions as Location-Based Services, the impact of hazards or nuisances on urban
areas, or analyzing the loads on urban infrastructure under different scenarios.
4.5 ProceduresTools for Generation of CityGML from IFC BIM
IFC is established as a generic information exchange model for BIM. It serves as an exchange format that has been adopted by many purveyors of CADBIM clients and
servers. There is a good deal of attention being given to the development of specific application views of IFC for particular domains of BIM, Notably the NBIMS, GSA BIM
standards initiatives in the U.S.; and INSPIRE in Europe, and BLISSABLE and Byggsok in Norway. Therefore we see that in the AEC world, IFC is a relatively stable
information model structure. Yet, IFC and BIM leave much to be desired in the
21 representation of building context. CityGML, on the other hand is establishing itself as a
very semantically rich and versatile information model for structuring information about contextual features and cities as a whole. While it is decidedly less detailed in
comparison with IFC, CityGML is well-adapted for representing those features that are apparent to such devices as airborne, ground-level, or interior. CityGML also provides
an appropriate level of semantic capacity that may be applied to the geometric aspects and their relationships with one another.
OWS-4 participants, including the principal developers and custodians of IFC and CityGML are in consensus that these two information models are complementary. While
each model has its distinct strengths within its area of focus, they also have areas of overlap. Therefore we believe that it is likely that some details of building context that
end up in an IFC model may have originated in a broader–scale CityGML model. Likewise, some building details that may be desired in a CityGML CityModel, such as
the gross building detail and up-to-date information concerning space use and occupancy, may originate in a BIM, exchanged as IFC.
AEC World Geospatial World
IFC CityGML
IFC Application View For Geospatial
OWS-5 CityGML
Buildings Rooms AEC World
Geospatial World
IFC CityGML
IFC Application View For Geospatial
OWS-5 CityGML
Buildings Rooms
Figure 4: IFC and CityGML Bridging Strategy
With this in mind, there is a great deal of value in the specification of specific content and methods for translating some subset of IFC to CityGML and vice-versa. There is a start
on this work already in the literature Liebich, 2004 and at the Forschungszentrum
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Copyright © 2007 Open Geospatial Consortium. All Rights Reserved
Karlsruhe Institute for Applied Computer Science Haefele, 2006
4.6 Architectures for Portrayal of Urban Landscapes
